Phoenix weather: 2017 was warmest year on record

Meteorologist Mark O’Malley talks about the above-average temperatures in Arizona and the bitterly cold weather in the eastern half of the U.S. and Canada. Tom Tingle/azcentral.com

Average daytime high temperatures in Phoenix usually top out the mid-70s this time of year, but current temperatures are pushing into the upper 80s and could flirt with 90 by Thanksgiving on Thursday.(Photo: Darrell Marquette /Special for The Republic)

Considering there were 96-degree days in March, near all-time highs in June and record heat on Thanksgiving, is it really a surprise that 2017 was the all-time record warmest year for Phoenix?

The average temperature (combining the average high and low and dividing by two) for the year was 77.3 degrees, according to the National Weather Service. That’s two-tenths of a degree higher than the previous record set in 2014. It's more than two degrees above the normal of 75.1.

If the Climate Prediction Center’s seasonal outlook proves to be accurate, 2018 could turn out to be a scorcher as well. The outlook for the first three months of the year calls for a 50-percent probability of above average temperatures continuing.

Changing climate a factor

Nine of the 10 warmest years for Phoenix have occurred since 2002 with the outlier being 1989.

Mark O'Malley, meteorologist with the National Weather Service in Phoenix, said the changing climate is the key factor in the warming trend.

"There were several weather events that made periods of the year much warmer than average," O'Malley said. "The underlying reason is obviously that we’re changing our climate and every year is warmer than the next. Add in the urban heat island and that exacerbates the problem."

The heat island effect (the abundance of concrete and asphalt in developed areas holds heat and doesn't allow things to cool off as much as undeveloped areas) contributes to the heat in Phoenix, but doesn't account for the increase in average temperatures in less developed areas. That points to an increasingly warm overall climate, O'Malley said.

"When all the rural sites match what’s happening in the city sites," O'Malley said. "That tells you it’s a warm year."

Numbers for the entire state are still being compiled, but O'Malley said the year should be one of the warmest ever for all of Arizona as well.

Warm nights

Warm nights were the main drivers of the record average temperature. The Urban heat island effect helps keep temperatures from cooling off much at night.

Sept. 8, 2014: According to Maricopa County's Flood District Storm Report, 3.3 inches of rain fell at Phoenix Sky Harbor International Airport. It was the most rain recorded on a calendar day since record keeping began around 115 years ago.
Michael Chow/The Republic

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Limited rainfall

The dry spell that has gripped the area since the end of the monsoon season helped make 2017 the 26th driest year for Phoenix. The official rain gauge at Phoenix Sky Harbor International Airport saw 4.96 inches of rain in 2017. Normal for that statistic is 8.03 inches.

The year was dry for the rest of the state as well. Things got off to a good start with rain and snow in the high country early in the year, but it didn't continue.

Mike Crimmins, an associate professor and climate scientist at the University of Arizona, said the disappointing precipitation would likely result in worsening drought conditions. The U.S. Drought monitor shows much of Arizona in moderate drought conditions but that is expected to change soon.

"We’re pushing a bunch of the drought categories down in Arizona," Crimmins said. "We're waiting for the December data to come in, but there is enough of the preliminary data from December to show it was not good."

As of Jan. 2, Flagstaff has not recorded measurable snow which will give this winter at least the fourth latest date for first snowfall in that city.

"It’s weird because in December Tucson had more precipitation than Flagstaff," Crimmins said. "That’s unusual, it’s kind of upside down as far as the precipitation pattern for December. It’s just been a weird fall and it looks like it’s going to be a weird winter."

Record heat

There were 14 high-temperature records set in 2017 including 96-degree highs on March 19 and 20, a high of 119 degrees on June 20 (tied for fourth-hottest day ever) and 87 degrees on Nov. 23 which tied the record for that date and for Thanksgiving.

Phoenix annual temperature rankings from the National Weather Service.(Photo: National Weather Service/Phoenix)